For example, as disclosed in WO-A1-2013/046259, JP-A-2015-118986, and JP-A-2008-4823, there is a printed circuit board on which a winding wire of a transformer or a choke coil is mounted.
In WO-A1-2013/046259, JP-A-2015-118986, and JP-A-2008-4823, a core of the transformer or the choke coil is used as a pair of upper and lower cores, and an E core which is formed into an E shape is used in at least one of the pair. In the E core, three leg portions are provided to be parallel to each other in one direction. Each leg unit is inserted into an insertion portion such as a penetration hole or a notch which is formed in the printed circuit board. The winding wire is wound around a middle leg portion to be fit into between the middle leg portion and left and right leg portions which are on left and right of the middle leg portions. The core forms a magnetic path of a magnetic flux which interlinks with the winding wire.
In WO-A1-2013/046259, a primary winding wire of a transformer is formed of a wiring pattern that is formed in each of surface layers which are disposed on both board surfaces of a multilayered printed circuit board, and a secondary winding wire is formed of the wiring patterns that are formed in a plurality of internal layers of the printed circuit board. The wiring patterns of the primary winding wires that are formed in the surface layers which are different from each other, are electrically connected to each other by a through-hole which is formed in the printed circuit board. The wiring patterns of the secondary winding wires that are formed in the internal layers which are different from each other, are electrically connected to each other by the through-hole which is formed in the printed circuit board. Since an electric current which is larger than that of the secondary winding wire flows through the primary winding wire of the transformer, a width of the primary winding wire is larger than that of the secondary winding wire.
In JP-A-2015-118986, a portion of a winding wire of a choke coil is formed of a wiring pattern which is formed in an internal layer of a printed circuit board, and the other portion of the winding wire is formed of a coil winding wire which is mounted on a surface of the printed circuit board. A portion and the other portion of the winding wire are electrically connected by a through-hole which is formed in the printed circuit board.
In JP-A-2008-4823, a first coil on a primary side of a transformer is formed of a wiring pattern which is formed in a printed circuit board, and a second coil on the primary side is formed of a winding wire that is mounted on an upper surface of the printed circuit board and has a small width. A coil on a secondary side is formed of a winding wire that is mounted on a lower surface of the printed circuit board and has a large width, and a winding wire that is mounted on the upper surface of the printed circuit board and has a large width, to be positioned above in comparison with the second coil on the primary side. An insulating sheet is disposed between the printed circuit board and the winding wire or between the winding wires. The wiring pattern and the winding wire, and the winding wires are electrically connected to each other by a through-hole which is formed in the printed circuit board.